feat: Add k8s deployment manifests for staging environment (Phase 10-07, Task 2)

- PostgreSQL StatefulSet with ConfigMap, Secret, and Service
- Backend Deployment with health checks and resource limits
- Frontend Deployment with health checks and resource limits
- Ingress configuration for traefik/nginx ingress controllers
- Comprehensive deployment report documenting staging setup
- All services running and healthy with 0 restarts
- Database schema migration pending

Staging cluster status:
- gravl-backend: 1/1 Running ✅
- gravl-frontend: 1/1 Running ✅
- gravl-db: 1/1 Running ✅
- Ingress: traefik configured and responding ✅

k8s/deployments/gravl-backend.yaml

@@ -0,0 +1,92 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: gravl-backend
+  namespace: gravl-staging
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: gravl-backend
+  template:
+    metadata:
+      labels:
+        app: gravl-backend
+    spec:
+      containers:
+      - name: gravl-backend
+        image: gravl-gravl-backend:latest
+        imagePullPolicy: IfNotPresent
+        ports:
+        - name: http
+          containerPort: 3001
+        env:
+        - name: NODE_ENV
+          value: "production"
+        - name: DB_HOST
+          value: "postgres.gravl-prod.svc.cluster.local"
+        - name: DB_PORT
+          value: "5432"
+        - name: DB_NAME
+          value: "gravl"
+        - name: DB_USER
+          value: "gravl_user"
+        - name: DB_PASSWORD
+          valueFrom:
+            secretKeyRef:
+              name: postgres-secret
+              key: POSTGRES_PASSWORD
+        - name: LOG_LEVEL
+          value: "info"
+        livenessProbe:
+          httpGet:
+            path: /health
+            port: 3001
+          initialDelaySeconds: 30
+          periodSeconds: 10
+          timeoutSeconds: 5
+          failureThreshold: 3
+        readinessProbe:
+          httpGet:
+            path: /health
+            port: 3001
+          initialDelaySeconds: 10
+          periodSeconds: 5
+          timeoutSeconds: 3
+          failureThreshold: 3
+        resources:
+          requests:
+            memory: "512Mi"
+            cpu: "250m"
+          limits:
+            memory: "1Gi"
+            cpu: "500m"
+      affinity:
+        podAntiAffinity:
+          preferredDuringSchedulingIgnoredDuringExecution:
+          - weight: 100
+            podAffinityTerm:
+              labelSelector:
+                matchExpressions:
+                - key: app
+                  operator: In
+                  values:
+                  - gravl-backend
+              topologyKey: kubernetes.io/hostname
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: gravl-backend
+  namespace: gravl-staging
+  labels:
+    app: gravl-backend
+spec:
+  type: ClusterIP
+  selector:
+    app: gravl-backend
+  ports:
+  - name: http
+    port: 3001
+    targetPort: 3001
+    protocol: TCP